Insights at the Ph-Based Hydration Regulation Mechanism of Supersulfated Cement

Supersulfated cement (SSC), mainly composed of solid wastes, is a highly promising low-carbon binding material, however, the application of SSC is still limited due to inherent defects in terms of strength and durability. In this paper, the influence of addition of different weak acid salts on the micro-structure and macro-performance of SSC has been investigated, and a pH-based mechanism for regulating the hydration process of supersulfated cement is proposed. The experimental results show that sodium lactate and low content of sodium citrate both promote the formation of hydration products AFt and C–S–H gel, which is beneficial to the improvement of frost resistance and the retention of strength in SSC. Furthermore, it is found that the dynamic adjustment of the pH value in the pore solution during the hydration process is a necessary condition for high performances of supersulfated cement, which can be realized by the weak acid salts. The high pH value in the early stage of hydration should be present to ensure the rapid dissolution of slag and gypsum, while the pH must be decreased to a certain value as the reaction proceeds, for the purpose of the stable growth of AFt. The mechanism interpreted here may pave the way for the mix optimization and broader application of SSC.